Process for producing pure lead carbonate from crude lead sulphate



Nov; is, 192a 159L841 NT oFFIcEf RENE nnnozn, or uccLn, nntrssnns, enteritis. rnocnss non rnonucme roan, LEAD CARBONATE anon canon LEAD smn'rn.

in Drawing. Application filed October 18,1926, serial No.' 142,527, and in France July'8,-19 26.

1 such as calcium'aetate and barium acetate,.

and renders such reaction a practical proposition by using an excess of alkali-earth.

metal acetate which, in the solution produced, prevents the reaction from being reversed. This solution contains, in addition 'l to the excess of alkali-earth metal acetate,-

the lead acetate formed in the said solution, and is treated with a base (preferably alkali-earth metal oxide or alkali-earth metal hydroxide corresponding to the alkali-earth metal, acetate used) to-form tri-basic lead acetate in solution which is decomposed with carbon dioxide to precipitate lead carbonate. The process canin particular be affected in such fashion that after the separation of the insoluble matter and/or the insoluble alkali earth metal sulphate, the addition of the bases and the precipitation of the lead carbonate by the carbon dioxide determines 5 the regeneration of'the initial solution 'employed for the treatment of the crude or impure sulphate of lead employed as the initial material. Y

Accor to one method of ca out the invention, a mixed solution is used which contains three equivalent parts of calcium acetate for one equivalent part of lead acetate. This mixed solution is caused to act upon crude lead sulphate (for example preliminarily neutralized slime from lead chambers) in the proportion of two equivalent arts of lead sulphate contained in the initia material to threeequivalent parts of lution.- The double-decomposition reaction is shown in the following equation:

(emotive thermostat] cream rac-so. (olmomoa 3[(0eEtofl)aPb] The insoluble matter comprising calcium sulphate formed in the course of reaction is separated with the aid of known means from the solution containing thelead acetate; the

, action and the molec may be dissolvedin reaction aid of. the solution ofcalcium acetate or of calcium acetate contained in the mixed soexcess (one equivalent part-in the present example) of calcium acetate prevents the reactionfrom being reversed. The stable solution is treated with milk of lime in the proportion of two equivalent "parts of calclum oxide or calcium hydroxide to three equivalent. parts of lead acetate insolutio'n. l Two equivalent parts oflead are thus .pre-- cip tated, '(i. e. two-thirds of the lead in solution) inthe forin of lead hydroxide whichv 1s,. as soon as it is formed, instahtlyTe-dis solved into trio-basic lead acetate by combin- 'inggwith the thirdQportion of lead which has remained in solution in the form of neutral acetate, so that the reaction is as follows:

n v emotion-a[(cimqart]4- canon):

'=-(o.n.o, 1 b-z1 b onh+a[ oimoa),o Lead in this-.reactionis convertnd into tri-basic lead acetate while the three mole-1 7 .cules of calcium acetate of the initial solution are simultaneouslyrecovered. The -li uid is'filtered to eliminate any possible 'ght excess of lime or of other. insoluble compounds whereafter the clear 30 solutlon is treated by a" streamof carbon dioxide produce the finalreaction;

a ime mice, (QIH'QIIPI) a [wimomoa] Lead carbonate is precipitated in this .re-

initial solution isrecovered: The lead carbonate thus formed is separated by filtration L and the resulting regenerated mixed solutioii' of lead acetate and calcium acetate'can be used again for dissolving crude lead sulphate. .i.

Should crude lead, sulphate to be treated also contain iron as an impurity the-latter l with the the mi'xed solution of lead acetate and calciumyacetate. In this case, precipitation;

caused by lime or an alkali-earth metal hydroxide leads to precipitation of dissolved iron in theform of insoluble tri-basic iron acetate which is separated in the filterin operation; preceding the precipitation (III of lead carbonate. Theloss' in acetate ontailed by this possiblyn preci 'itation of men may always be. compensa for.

by suitable additions o luble acetates made I e oflea'd acetate ofthe before the regenerated mixed solution is used igam. I v

Having thus described my invention, what I claim and desire to secure by Letters Patent is T1. A process for the manufacture of pure lead carbonate, comprising the steps of treating crude lead sulphate (for example, slime from lead chambers) with a solution of alkali-earth metal acetate the bases of which form insoluble sulphates such as calcium acetate, barium acetate, etc., in excess to efiect a double'decomposition between the lead sulphate and said alkali-earth metal acetate, separating the resulting solution from the insoluble matter (comprising insoluble alkali-earth metal sulphate derived 'from the said double decomposition), treatalkali-earth metal acetate, separating the resulting solution from the insoluble matter (comprising insoluble alkali-earth metal sulphate derived from said double decomposition), treating the separated solution with an alkali-earth metal base'; decomposing'by carbon dioxide the t-ri-basic lead acetate formed in solution thereby precipitating lead carbonate; and regenerating the initial solution containing lead acetate arid alkalineearth acetate and separating the lead carbonate from the regenerated solution.

3. In a process according to claim 2, using a mixed solution containing three equivalent parts of calcium acetate. (O H O Ca] for one equivalent part of lead acetate [(C H O' Pb], in theproportion of two equivalent parts of lead sulphate contained in the crude lead sulphate material treated; treating the resulting solution separated from the insoluble matter with two equivalent parts of calcium hydroxide [Ca(OH) decomposing by carbon dioxide one equivalent art of tri-basic lead acetate [(C H Pb.2l?b(OH) formed in solution thereby precipitating lead carbonate and reforming thesaid initial mixed solution and separatin the lead carbonate from the regenerated so ution.

In testimony whereof I aflix my signature.

RENE DALO'ZE. 

